Don't count suspended users in user count (mastodon#9380)

Fix mastodon#7637

Author: Gargron

app/presenters/instance_presenter.rb

@@ -18,7 +18,7 @@ def contact_account
   end
 
   def user_count
-    Rails.cache.fetch('user_count') { User.confirmed.count }
+    Rails.cache.fetch('user_count') { User.confirmed.joins(:account).merge(Account.without_suspended).count }
   end
 
   def status_count